1. Field of the Invention
The present invention relates to determining the relative location of components of a printing apparatus, for example a large format printer. In particular, in inkjet printers having a printhead service station, there is a need to accurately position the inkjet printheads relative to their respective service station cartridges.
2. Description of the Related Art
The service station is an essential subsystem in printers based on thermal inkjet technology (TIT). Its main purpose is to maintain optimal print quality and to do so, it can act on the printhead or pen in different ways (such as wiping, spitting . . . ). These actions are termed xe2x80x9cservicing primitivesxe2x80x9d. They are arranged in complex sequences (servicing algorithms), that are executed in response to various triggers.
The functions a service station provides depend on the architecture, but as the printhead complexity increases, more and more sophisticated features need to be implemented. For instance, in the present printing apparatus there may be up to eight different xe2x80x9cprimitivesxe2x80x9d, namely: capping, spitting, wiping, PEG (i.e. the application of polyethylene glycol liquid), scraping, snout wiping, priming and drop detection. Since the volume occupied by the service station is much the same as in previous products and because more functionality has been added, there is less space available for each xe2x80x9cprimitivexe2x80x9d.
The servicing functions can work correctly with a maximum placement error of 0.8 millimeters for the scan axis. The service station axis substantially perpendicular to the scan axis is somewhat more tolerant accepting up to 1.5 millimeters. Unfortunately, the mechanical tolerances alone, while meeting the goal in the service station axis, are unacceptable for the scan axis (the worst-case placement error is 1.4 millimeters).
Therefore, a method of reducing tolerance problems along the scan axis is required. One possible way would involve an expensive production process with better tolerances. An alternative is to calibrate the error out of the system. This determines the physical position of the components and adjusts each function based on this measurement.
The printers in the series HP Designjet 2000 and 2500, first marketed in March 1997, adopted the solution of placing an optical reference mark on the service station housing which is scanned by an optical sensor mounted on the printer carriage. This did not allow for any tolerances between the housing and the position of the service station cartridges within the housing. Moreover, no measures were taken to allow for possible variations in the relative positions on the printer carriage of the optical sensor and the printhead cartridges. Such prior art printers are disclosed in U.S. patent application Ser. No. 09/031,115.
EP-A-0863009 discloses an optical encoding arrangement incorporating a marker for orientation on a service station carriage and a label for carrying information related to service station functions. The service station module may incorporate holes for storing and conveying information.
The present invention seeks to overcome or reduce one or more of the above problems.
According to a first aspect of the present invention, there is provided a method of determining the relative location of a component of a printer apparatus with respect to a printhead carriage of the printer apparatus, said component comprising one or more sub-units co-operating with a corresponding number of printheads on the carriage, wherein a sensor is used to determine the position of a reference location on said component relative to the sensor, characterised in that the sensor is also used to determine the position of at least one printhead relative to the sensor.
According to a second aspect of the present invention, there is provided a method of relatively locating at least one component of a printer apparatus to a printhead mounted on a printer carriage, wherein a sensor mounted on the carriage is used to scan a reference location on the component, characterised in that there is also determined the relative location of the optical sensor to the printhead on the printer carriage.
The sensor is preferably an optical sensor and, to determine the relative location of the optical sensor to the printhead (K), the printhead is caused to print during a carriage movement a reference mark extending substantially in the direction of the media axis, and the optical sensor subsequently scans the reference mark along the scan axis and there is determined therefrom the sensor to printhead distance (xe2x80x9cjxe2x80x9d) in the direction of the scan axis. The reference mark is preferably a straight line.
In a preferred method the step of determining the sensor to printhead distance (j) is preceded by causing the printhead (K) to print a reference mark in the direction of the scan axis, then using the optical sensor to scan the reference mark along the media axis of the printing apparatus, and then determining the sensor to printhead distance (r) in the direction of the media axis and taking into account its effect on the determination of the sensor to printhead distance (j) in the direction of the scan axis. The reference mark extending in the direction of the scan axis is also preferably a straight line.
According to a third aspect of the present invention, there is provided a method of determining the relative location of at least one printhead mounted on a printer carriage with respect to one or more service station insert members mounted in a service station, the method using an optical sensor mounted on the printer carriage. characterised in that the sensor detects a reference location provided on at least one of said service station insert members. The insert members are preferably cartridges which perform various servicing functions and may each be associated with a respective printhead.
According to a fourth aspect of the present invention, there is provided an inkjet printing apparatus comprising one or more printheads mounted on a printer carriage and means for determining the position of at least one other component of the printing apparatus relative to the or each printhead, said determining means comprising a sensor mounted on the printer carriage, characterised in that calibration means are provided which determine the relative positions of the sensor and the or each printhead. The sensor is preferably an optical sensor.
According to a fifth aspect of the present invention, there is provided an inkjet printing apparatus having means for locating one or more printheads mounted on a printer carriage with respect to one or more respective service station insert members mounted in a service station, the apparatus comprising an optical sensor mounted on the printer carriage and means defining one or more reference locations within the service station area, the reference locations being optically detectable by the optical sensor, characterised in that the or each reference location is provided on a respective service station insert member.
Preferably each reference location is constituted by a through a hole in a part of the respective service station insert member, e.g. in its handle or lid.
Preferably, each service station insert member has a respective reference location. These locations may be averaged to reduce any residual errors.